Polymeric compositions borne in organic solvents rely on solvents or solvent blends to control the drying characteristics of the compositions, according to the application requirements. The disadvantages of such organic solvent based compositions are the difficulties of clean-up, the toxic nature of organic solvents, environmental pollution, health hazards due to toxic solvent fumes, and the relatively high cost of organic solvents that are ultimately wasted.
Water-containing polymeric products such as water-borne paints and water-based flexographic, gravure, and screen printing compositions find increasing utility due to their safety, and economy. Furthermore, they tend to be environmentally sound, since they tend to have small amounts of solvent, that is, typically between 10% and 35% solvent by weight. However, water-based screen printing inks have a history of being difficult to process, exhibiting problems, such as drying and plugging up printing greens, poor adhesion to vinyl and acrylic substrates, poor outdoor durability, poor printing quality, that is, ink flow and leveling problems, and limited long run capability.
Some conventional flexographic and gravure water-based inks typically have 10% or less by weight organic solvents, primarily alcohols. In these printing methods, the inks are printed on a rotary press at fast speeds where drying is not a problem. Usually, these water-based inks dry too slowly for these methods.
However, drying characteristics of screen-printing water-borne compositions are variable and not easily controllable, since the characteristics are tied to the evaporation characteristics of the water and organic solvents. The inability to control evaporation characteristics can lead to poor quality of a screen print, impaired efficiency of the screen due to ink skimming, that is, dried ink on the surface of the ink reservoir, and increased down-time of the printing equipment necessary to remove residually dried inks.
Coalescing aids are commonly used in screen printing inks and some examples of coalescing aids typically used include hydrocarbons, alcohol esters, glycol ether esters, glycol ethers, and glycols. However, this additive can be costly and is an organic solvent with all the disadvantages associated with organic solvents.